Hib Halverson's Big Block From Hell Series

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Part 2...Cylinder Head Art and Science

by Hib Halverson

In this second part of the Big-Block from Hell series, first, we are going to finish
assembling the short block, then we will examine proper modification of oval-port,
big-block heads for street high-performance use.

Short block wrap up

When we left Edelbrock in Part One, preliminary short block operations were complete
and our engine assembler, Mike Eddy, had installed the crankshaft.

The chamfer on the big end of each Crowerod must face the outside of its respective rod
bearing journal and Bill Miller Engineering pistons must have their domes oriented
correctly. Thus, four rod/piston units are assembled one way and the remaining four the
opposite way. This all sounds pretty damn complicated but, there is an easy way to get it
right. Just remember: the numbers on the rods' big ends go to the outside and the domes go
to the outside, too; or as Mike Eddy says, "nado" for "numbers and domes
outside." Apply Red Line Assembly lube on the wrist pin and the rod's small end,
orient the rod and piston such that all is "nado" then slide the wrist pin in
place. Pretty slick, eh?

To retain wrist pins, BME pistons use four Spiralocs. They're devilishly hard to
install. Use your fingers to slightly spread the ends of the Spiraloc apart then, with a
rotating motion, feed it into the pin lock groove. You must do this four times for each
piston. It comes with experience is all I can sayÉwhile Mike Eddy did six pistons, I was
only able to assemble two.

The Big-Block from Hell's 454 uses a Childs and Albert ZGS piston ring set.
"ZGS," an acronym for "Zero Gap Second," denotes C&A's
torturous-leak-path, second ring design. A ZGS ring does have a "gap" but it
consists of two overlapping steps with an inner boot "back seal". Use of ZGS
rings with properly prepared cylinder walls will pay off in reduced cylinder leakage.
(author's note: this article is reproduced, for the most part, as it was printed in Vette
Magazine back in 1991. There were, in fact, serious problems discovered later with the ZGS
rings and they will be covered in a future part of the series.

The oil ring goes on the piston first. Make sure the two oil rail gaps are positioned
opposite each other and that the ends of the expander butt together 45degrees from either
of the rail gaps. The ZGS "inner boot" is installed in the second ring groove
followed by the ring itself. The assembly must have a minimum of .005" back groove
clearance and its gaps must be opposite each other. If back groove clearance is lacking,
you have two choices.

1) Use the ring without the inner boot. The effect of the ZGS ring will be reduced but not
eliminated or
2) have the second ring groove on your pistons machined for more depth. Last to go on is
the plasma/moly-filled, ductile iron top ring.

Mike Eddy determined last month that we would use Childs and Albert, .001"
undersized rod bearings. The Crowerrods were fitted with upper bearing shells then the
piston skirts and the rings were given a light coat of Red Line Break-In Oil. The
rod/piston units were installed in specific cylinders (selected last month) using a
B&B Performance tapered ring compressor (p/n 4145). Superior to
"squeeze-type" units, B&B Compressors taper to your exact bore size, are
made of hard-anodized aluminum and come in a multitude of diameters. The piston can be
driven smoothly by hand through the compressor and into the cylinder. The rod caps were
fitted with bearings, installed onto the rods and had their bolts torqued to 65 ft/lbs.

The camshaft will be a critical factor determining whether or not this engine will meet
its power and drivability goals. An Edelbrock Torker-Plus hydraulic lifter cam (p/n 5062)
will replace the Melling 396-S used previously. Compared just by duration and lift, the
two appear somewhat similar.

Stock Chev. 3883986

Melling 396-S

Edelbrock 5062

Duration at .050" lift~Int./Exh

213o/217o

222o/235o

224o/232o

Valve lift~Int./Exh.

.460/.480"

.500"/.505"

.527"/.553"

However, the 5062 has significant differences: 1) a moderate lift increase to which the
big-block responds particularly well 2) more rapid valve opening and closing rates. For a
given duration, the valve will be open a greater amount 3) although it works well in any
oval-port big-block, the Edelbrock cam really shines with cylinder heads that have been
mildly ported and polished and 4) to capitalize on the interaction between intake manifold
and camshaft, the Torker-Plus was developed in conjunction with Edelbrock's Torker 2-O
manifold, which we also will be using.

The camshaft was treated with G&L Coatings' DFL0221 dry film lubricant then
burnished with a Standard Abrasives General Purpose Brite-Rite pad. G&L DFL0221 and
its preparation before use were discussed at length last month.

Mike Eddy spread Red Line Assembly Lube on the lobes and bearing journals of the 5062
then slid it in place. Installation of an Edelbrock True-Rolling Timing gear set (p/n
7810) finished the job. Next month, once the rest of the valve gear is fitted, we will
discuss the camshaft checking process.

The last short block assembly tasks dealt with the oiling system and Mark Gray stepped
in the do the honors. He began with a Milodon oil pump (p/n 18760) that was prepared for
use by coating the interior of the pump body and its gears with G&L DFL0221,
chamfering the area were oil flow transitions from the pump body to the output line and
shimming the pressure relief valve spring .025-inch. The pump was then fitted with a
B&B High Strength pump drive shaft (p/n 6508) and a special Milodon oil pump pickup
(p/n 18465) designed to work with a Milodon oil pan we will install later. The pickup is a
heavy press fit into the pump body and also bolts to the oil pump cover so welding it into
the pump body was unnecessary. A B&B Oil Pump Stud Kit (p/n 3400) was fitted to the
short block and a Milodon windage tray (p/n 32200) was attached to the ends the main
bearing cap studs.

This tray requires trimming where it mounts at the oil pump and the nuts used to fit
the tray to the main studs must have their height set. The best way to do this is first,
fit the tray at the pump, then lower the oil pump and windage tray into place as a unit.
Hand tighten the rear nut, set the height of the lower tray nuts then add lock washers and
upper nuts tightening them to 35 ft/lbs. Tighten the oil pump stud nut to 65ft/lbs. With
that, Mark Gray covered the short block with an engine bag. We will be back to it in Part
3.

Cylinder Head Preliminaries

The reasoning behind porting, polishing and custom valve jobs is simple. Those
techniques reduce resistance to flow in and out of the combustion chamber. Anything done
to enhance flow makes the engine more efficient and powerful. Thus, the heads are another
big factor in how well the BBfH 454 will perform.

Mark DeGroff's Cylinder Head Service and Machine Shop is one of those small, unique
firms whose work is as much science as it is art. DeGroff learned the cylinder head craft
at Valley Head Service for almost 20 years ending as General Manager in 1980. In Ô81 he
opened his own operation and has never looked back. His three-man shop offers personal
service and attention to detail that is difficult to find but expected by many Corvette
enthusiasts.

From the BBfH 454, we want plenty of low-end torque and a 5500-6000 rpm power peak so
we are using the stock, 1971, low-performance, oval-port head castings (DeGroff calls them
"truck heads"Ésuch abuse we take in the name of bringing you a great engine
project!). Why "Lo-Po" heads? Well, first they're cost effectiveÉlike, we
already had themÉalso, their smaller intake port volume is well suited to a stump-puller,
six-grand big-block.

Mark DeGroff's port and polish strategy would be to moderately increase air flow by:

1) an increase in both intake and exhaust valve sizes,
2) porting of the valve pockets
3) smoothing of the short-side radii of both intake and exhaust ports and
4) streamlining and polishing of both the intake port entries and the exhaust port exits.
This combination, an excellent compromise between power increase and cost, is known as a
"street port and polish".

The castings were hot tanked and pressure checked. Mark then inspected the valve guides
for excessive stem-to-guide clearance. The guides in cast iron big-block heads are quite
durable. Even our high mileage units showed no significant wear. We would leave them
untouched. Next, to check if the head gasket surfaces were parallel to the planes of the
head castings, Mark carefully measured the height of the gasket surface on each head at
the three locating pads that Chevrolet uses to index all of their machine work. One head
was acceptable, the other was tapered approximately .010". Lack of parallelism would
be corrected later.

Our DeGroff heads will be fitted with larger diameter, Milodon Megaflow Competition
intake (p/n 45115) and exhaust (p/n 45135) valves. They are made of stainless steel, have
stock diameter stems, hardened tips, hard-chromed stems and swirl polished heads. The area
of the stem just above the head is of reduced diameter to improve air flow.

The valve seats were bored out to fit the L-88/ZL-1 sizes of 2.190" and
1.880" respectively. Next Mark rough finished the new valve seats with a Kwik-Way
valve seat grinder fitted with a 45o stone.

Mark set the valves in place and made the initial seat depth measurement. Additional
small amounts of seat grinding were done to set depths within .010". This is
necessary as valve seat depth affects porting around the seats and polishing of the
combustion chamber. Valve seat depth will get a fine adjustment during the CC'ing process.

Porting

We cannot overemphasize the importance of experience in head porting. Inexpensive
do-it-yourself or "home" porting kits are available containing some of the tools
and materials that those who port heads for a living use. However, these kits contain no
"instant expertise." We suggest, unless you have substantial porting know how or
a large supply of castings, a flow bench and many hours to spend on the learning curve;
that you skip the home porting kits and have professionals do the work.

Mark DeGroff begins porting with the intake valve pocket or "bowl," as the
experts say. This area is enlarged bringing its diameter out to just under the valve size.
Next, the intake port short side radius is blended and smoothed. This is a critical flow
area as it is where the floor of the port curves down to the valve seat. The port entry is
not enlarged as we want only moderate cross-sectional area to keep flow velocity high for
good mid-range torque and sharp throttle response. Intake manifold port matching is
usually done at this point, however, Edelbrock recommends the Torker 2-0 be used without
port matching.

Big-block Chevrolet exhaust ports have, relative to the intakes, poor airflow
characteristics. Some of the flow improvement we need will come from the 1.88-inch valve.
In addition, to bring the exhaust/intake flow ratio from the 65% of a stocker to around
the 80% considered appropriate for street high performance or racing engines; port work
similar in nature to that done on the intakes was necessary.

Polishing

Intake and exhaust port surfaces are polished using different techniques. Intakes are
finished with rotary stone in the die grinder which leaves a surface that is noticeably
dull and rougher. In pre-flow bench times, everything was near-mirror finish. Flow testing
done in the '60s and early '70s discovered that with intake ports, this finish was
detrimental. A very smooth port wall causes much turbulence restricting flow in the main
part of the air stream.

If the intake port wall is finished such that it is smooth, but not "very
smooth" the slight roughness actually decreases turbulence and allows a
"boundary layer" of smooth air to form next to the wall. The main part of the
air stream can "slide" over this boundary layer and air flow numbers improve.

Conversely, Mark DeGroff polishes the exhaust ports to near-mirror finish with his die
grinder fitted with a 60-grit Standard Abrasives sanding cartridge roll. Port wall finish
is not important as velocity in the exhaust ports is about four times that in the intakes.
A very smooth finish reduces carbon build-up on the exhaust port walls.

The combustion chamber walls were altered to match the profile of the cylinder tops in
the block left last month after the block was relieved. After that, Mark polished the
combustion chambers using Standard Abrasives 60-grit "SocAtt¨" sanding discs.

Valve Job and CC'ing

The first step here was to machine the head gasket surfaces to correct the lack of
parallelism discussed previously. The head with the problem got a .012" angle cut and
the other "straight" head took a .002" cut. Mark DeGroff explained that the
surfacing operation is concluded before grinding the valves and valve seats as the final
valve seat depth measurement and the combustion chamber displacements depend on this
parallelism.

The value of a multi-angle valve job to a set of street high-performance or racing
heads is undisputed. It is a critical factor to improved flow at low valve lifts. The
ideal situation would be to have smoothly radiused valve faces and seats however, there
would be no place for the valve and seat to seal. The next best thing is a series of
straight cuts at a number of different angles. The angles are selected so the air flow
will "see" the angles as nearly a smooth radius.

With our DeGroff heads, the intake seats get 45o, .060-inch wide cuts and the exhausts get 45o, .080" cuts. This is
done with a 45o stone on the Kwik-Way valve seat grinder. Next, the valve depths are measured
again and, if necessary, the seats are ground slightly to get depths within .002" of
each other. Finally, all valve seats get a 60o under cut and a 35o top cut. The valve faces are ground on a IDL valve grinding
machine. The intake valve has a 45o, .060" wide face cut and a back cut of 35o. The exhaust valve gets a
45o,
.080" wide face cut followed by a 25o back cut.

Valve lapping is next. This time-honored final touch, optimizes the seal between the
valve and seat. An ultra-fine abrasive paste known as "lapping compound" is
spread on the valve face. The valve is put in place and spun using a
suction-cup-with-handle device. In addition to honing the seats and faces, the lapping
compound leaves behind a gray haze giving a final indication as to the quality and
positioning of the valve-to-seat contact area.

It is necessary for all the combustion chambers to be of equal displacement. To get to
this point, each chamber must have its displacement measured then, if their numbers vary
too widely, adjustments must be made to equalize the numbers. The largest chamber is
selected then, the remaining seven chambers have small amounts of material removed such
that are all within 0.25 cc of each other. Our final average chamber displacement was
113.5cc's.

Flow Testing

No serious cylinder head modification shop works without a flow bench to simulate and
measure airflow through intake and exhaust ports. Mark DeGroff has a Superflow 110 flow
bench he uses to do R&D and spot check his cylinder head work.

The first step was actually taken before Mark made any changes. After cleaning one of
our castings, he flow tested the stock ports. All big-block heads, excepting the Bow Tie
aluminum race head (p/n 10051128), have two different intake ports. The "good
ports" aim directly at the valve. The "not so good ports" are shorter but
curve to clear pushrods. Proper intake port flow testing procedure is to flow test the bad
ports. You can figure that the good ports will always be better.

On the Superflow 110, our DeGroff heads showed a 12.3% average increase in intake flow
and a 30.6% average increase in exhaust flow. The difference in increases is because the
stock intake ports are quite efficient, considering their port volume and valve size,
where as the stock exhausts are not as good. Thus, the street port/polish procedure has a
more pronounced effect on the exhaust port. Admittedly, a small additional increase can be
had with porting the intake further, but it would come at greatly increased cost.

Cylinder head flow comparison c/n 3993820

Valve lift (inch)

.050

.100

.200

.300

.400

.500

Stock Chevrolet "bad" intake

Air flow (cfm)

18.5

35.4

72.5

113.3

129.9

139.5

DeGroff modified
"bad"intake

Air flow (cfm)

20.6

41.6

86.0

118.2

143.1

156.3

Stock Chevrolet exhaust

Air flow (cfm)

13.4

25.8

52.7

71.9

87.9

95.2

DeGroff modified exhaust

Air flow (cfm)

16.7

33.5

70.9

95.6

113.3

128.6

Finally

All these numbers mean much to cylinder head aces like Mark DeGroff. They sit around at
parties talking about how they got such-and-such a port to flow three more cfm at .825
valve lift. However, with most of us Big-Block drivers, what counts is how we feel when we
hit the loud pedal! We'll find out how good Mark's work is when we put the Big-Block from
Hell's on the dynamometer in Part 4 of our series due in the November Vette.

Flow testing complete, it was time to deburr the inside and outside of the heads.
Particular attention was paid to removing casting flash, rust and scale from oil
drain-back holes and coolant passage openings. The castings were then thoroughly cleaned
and blow dried. Cylinder head assembly began with the installation of new B&B
Performance rocker arm studs (p/n 3615) and the set of Chevrolet pushrod guide plates
removed during the disassembly process in Part 1.

Next the valves' stems were coated with Red Line Assembly Lube and fitted to the heads.
Edelbrock retainers (p/n 9731) and Stem Locks (p/n 9611) only were set in place to allow
DeGroff to check the valve spring installed height. We are using Edelbrock Torker Series
Valve Springs (p/n 5762). They go with the 5062 camshaft and must be installed at
1.870". Mark found that the installed heights in several locations were
.060-070" too low, a problem typical of stock heads. Low installed height will have
valve spring seat pressure above the Edelbrock specification of 110-120 lbs. This causes
excessive pressure on the cam lobes at valve opening and possible premature camshaft wear.
The solution was time consuming but nevertheless, necessary. DeGroff machined the valve
spring seats such that the installed height of all springs was the desired 1.870".

After a repeat visit to the solvent tank, it was back on the assembly bench. The
Milodon valves were reinstalled and as our heads had been previously equipped with Perfect
Circle valve stem seals, a new set was put in place. The Edelbrock springs were checked
for open pressure (int. 290 lbs@.527" and exh. 300 lbs@.553") then installed
followed by retainers and locks.

To improve oil drain back, areas exposed to engine oil were painted with General
Electric "Gyptal" armature paint. External surfaces were sprayed with Chevrolet
orange. When dry, Mark DeGroff put the heads in plastic bags for shipment to Edelbrock.
Next month we will detail the rest of the engine assembly process.